The present invention relates to an apparatus and a method for transferring heat between one or more heat transfer surfaces and a heat carrier medium in either a liquid or two-phase state, particularly for cooling of electronic devices.
Heat dissipation in technical devices, particularly in electronic devices such as power electronic devices, microprocessors or lasers, imposes serious issues regarding the design of technical systems, particularly with respect to system integration and performance. To avoid overheating of these devices, cooling measures are commonly applied. Owing to the increasing power density of such devices, cooling methods have steadily developed.
Most technical systems, in which cooling of a high-power density device is required, utilize a cooling medium that is forced to stream over a cold plate of a device or a surface coupled thereto, so that heat dissipated by the high-power density device is transferred to the cooling medium.
In contrast to air as a heat carrier medium, usage of liquids requires creation and organization of passageways within enclosed volume of a heat exchanging apparatus. Hence, such apparatuses become increasingly complex as the amount of thermal energy to be transported increases. Usually increase of heat exchange efficiency is achieved by turbulization of the flow that causes higher hydrodynamic losses within a cooling device. In view of a minimum flow rate required for transporting heat away from or towards to a serviced device, these hydrodynamic losses negatively affect the system, requiring bigger, more powerful pumps, increasing system's noise level and power consumption, and decreasing its reliability and uptime.
As increasing the transfer surface between the cooling liquid and the device to be cooled turned out not to be sufficient in high-power density devices, new techniques have been developed recently to cope with managing high heat densities of devices to be cooled. For instance, synthetic jets have been developed which are based on piezoelectric vibrations applied to the cooling liquid.
Furthermore, impingement jets are used which include jet streams of a cooling medium that are directed to a heat transfer surface. The cooling medium experiences a significant turbulization in the vicinity of the heat transfer surface which might result in an uneven heat transfer from the heat transfer surface, so that localized hot spots with reduced heat transfer characteristics will occur. This effect is even more dominant for higher jet velocities and/or inlet pressures.
For lower velocities, impingement jets have a more laminar flow with no or a low swirling tendency and therefore only a low heat transfer rate to the cooling medium due to the formation of a boundary layer between the jet and the heat transfer surface is obtained.
Artificial turbulization of the flow inside heat exchanger allows to achieve heat transfer rates common for turbulent flow at much lower velocities, and therefore with much less energy and much higher reliability. To achieve such an effect the swirling of a jet is essential. In document US 2011/0042041 A1, this has been achieved by directing jets with opposite flow directions over a heat dissipation surface in an interleaved, i.e. in a comb-shaped manner, so that the jets pass side by side with neighboring jets having transverse flow directions. Between two neighboring jets, vortices are generated which destroy the boundary layers between the jet and the heat dissipation surface and thereby improve the heat dissipation. However, the hydrodynamic losses are high due to alternating streams and a complex structure requiring low tolerance is necessary for generating those interleaved jets.
In view of the above, it is desirable to provide a heat transfer from or to a heat transfer surface by means of a heat carrier medium in a liquid or a two-phase state flowing along the heat transfer surface while providing low hydrodynamic losses and uniform heat flow rate, i.e. by avoiding local hot spots.